Multichip circuit modules or simply “circuit modules” are self-contained packages containing all semiconductor dies and other electronic components housed in the package. The package includes suitable electronic interconnection points, such as leads, lands, solder balls, etc., to enable the circuit module to be electrically and physically connected to another printed circuit board, such as a motherboard in a personal or tablet computer system or in a smart phone. A power module, for example, is a circuit module including all chips or dies (e.g., a controller die) and all other electronic components (e.g., power MOSFET transistors, phase inductors, and required resistive and capacitive components) housed together in a single package to form a desired type of power supply.
A circuit module includes some type of package substrate on which the semiconductor dies and other electronic components are mounted. The package substrate provides both for physical mounting and the electrical interconnection of the components. The type of package substrate utilized is typically determined based on a number of different factors, such as the cost of the package substrate, the wire or trace routing capability the package substrate must provide, and the thermal conductivity of the package substrate. For example, the package substrate could be a dual layered or even multilayered printed circuit board that would provide good routing capability for electrical interconnection of the components but would be relatively expensive and would not provide good thermal conductivity. This latter factor, thermal conductivity, is of particular concern in applications that dissipate a relatively large amount of power, such as where the circuit module is a power module. Where the power module is a switching regulator such as a DC-to-DC converter, the power MOSFET devices and inductors generate a relatively large amount of heat, and the thermal conductivity of the package substrate should be high enough to adequately dissipate this generated heat.
Existing power modules utilize a variety of different types of package substrates, each package substrate providing corresponding advantages and disadvantages in terms of the routing capability, thermal conductivity, and cost. Once such package substrate is a dual layered printed circuit board in a land grid array (LGA) power module. With such a dual layered printed circuit board, the routing capability to provide all the required electrical interconnections is good. The thermal conductivity, however, is undesirably low due to the relatively low thermal conductivity of the core material of the dual layered package substrate. Another approach is known as a quad flat no leads (QFN) power module in which the package substrate is a metal lead frame. In this approach, the metal lead frame provides very good thermal conductivity but relatively poor routing capability. To improve the routing capability of a QFN power module, another approach utilizes a tiny internal printed circuit board (PCB) to which controller and some resistive and capacitive components are directly coupled, with the internal PCB containing these components then being coupled to the metal lead frame. The internal PCB improves the routing capability among the resistive and capacitive components and the controller, and the thermal performance of such a module is good. The routing capability between power components not on the internal PCB remains poor, however, and the internal PCB also increases the cost. Yet another approach utilizes what is known as backside molding to cover portions of the bottom of the metal lead frame and provides more flexibility in the location of pads of the metal lead frame for interconnection to the printed circuit board to which the power module is attached. Due to the single metal lead frame this approach too suffers from relatively poor routing capability.
There is a need generally for improved circuit modules, and in particular improved power modules having good routing and thermal capabilities at a low cost of manufacture.